Scheduling method for wireless packet data channel

ABSTRACT

A scheduler at a base station may schedule packet data traffic based on a ranking metric that varies directly with the mobile station&#39;s scheduling downlink transmission rate and a delay factor indicative of the staleness of the corresponding queued data. The ranking metric may advantageously vary in a direct non-linear fashion with the delay factor to allow for delay sensitive data, such as VoIP data, to be scheduled with increased urgency when quality of service is about to be compromised. The scheduler may attempt to pack a multi-user downlink physical layer packet by selecting a tentative rate and determining if an aggregate amount of data in the packet may be increased by transmitting the packet at a lower rate. If so, additional queued data is added to the packet and the transmission rate for the packet is lowered. Such an approach allows for greater link efficiency to be achieved.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication 60/629,544 filed Nov. 11, 2004, which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

The present invention relates to mobile communication systems; and, moreparticularly, to methods of scheduling a time shared downlink packetdata channel.

The demand for wireless data services, such as mobile Internet, videostreaming, and voice over IP (VoIP), have led to the development of highspeed packet data channels to provide high data rates needed for suchservices. High speed packet data channels are employed on the forwardlink in IS-2000 (also known as 1xEV-DV), IS-856 (also known as 1xEV-DO),and Wideband Code Division Multiple Access (WCDMA) systems. The highspeed packet data channel is a time shared channel. Downlinktransmissions, e.g., from a base station to the mobile stations, aretime-multiplexed and transmitted at full power.

At any given time, the base station may transmit a packet to one or moremobile stations on the physical layer channel known as the downlink highspeed packet data channel. Deciding which mobile station(s) to servewith the packet at a given time is the function of a “scheduler.” Anumber of different scheduling strategies can be used, each with adifferent implication for system throughput and fairness. Typicalscheduling strategies employed include round-robin, maximum throughput,and proportional fairness. In addition, quality of service requirementsfrequently add scheduling complexities. For example, VoIP packet data,due to its conversational characteristic, typically has a relativelyshort maximum allowed transmission delay before service is considered tohave unacceptably degraded. Thus, it is commonly necessary to scheduleVoIP packet data for transmission more frequently than other packet datain order to maintain acceptable service.

However, simply scheduling VoIP packet data more frequently, withoutmore, may result in inefficient use of available resources. This isbecause VoIP data is typically supplied at relatively low rate. As aresult, VoIP data queued for transmission to a particular mobile stationis typically less than a full packet's worth of data. Thus, if only thatVoIP packet data is transmitted in a given physical layer packet, thepacket is likely less than full, and typically significantly less thanfull. Transmitting less than full packets, particularly relativelylightly loaded packets, unnecessarily consumes available systemresources, and may result in a degradation to the service provided tothe other mobile stations being served by a given base station.

Thus, there remains a need for alternative scheduling and/or packetfilling techniques, advantageously techniques that are better adapted tothe downlink transmissions of VoIP data on high speed packet datachannels.

SUMMARY OF THE INVENTION

In one embodiment, a scheduler, typically having one or more processingcircuits and forming a portion of a base station, schedules use of adownlink packet data traffic channel shared by a plurality of mobilestations by ranking at least some of the mobile stations based on delay.The scheduler employs a scheduling approach that comprises: calculatinga ranking metric for a mobile station that varies directly with themobile station's scheduling downlink transmission rate and a delayfactor indicative of the staleness of the data queued for the mobilestation; and scheduling one or more downlink transmissions to the mobilestation on the packet data traffic channel based on the ranking metric.The ranking metric may advantageously vary in a direct non-linearfashion with the delay factor. The calculating the ranking metric maycomprise calculating the ranking metric as a function of the schedulingrate divided by the difference between a threshold and the delay factor.The threshold may represent the maximum allowed delay, and the delayfactor may be based on an amount of elapsed time associated with theoldest of the data queued for the mobile station. In some embodiments,the ranking metric RANK varies according to the formulaRANK=R/(d_(max)−d)^(k), where R represents the mobile station'sscheduling downlink transmission rate, d_(max) represents the thresholdvalue of the maximum allowed delay, d represents the current delayfactor, and k is a sensitivity exponent. K may equal one. The delayfactor may be based on an amount of buffer consumed by the queued data.In some embodiments, the ranking metric RANK varies according to theformula RANK=R/(q_(max)−q)^(k), where R represents the mobile station'sscheduling downlink transmission rate, q_(max) represents the thresholdvalue of the maximum allowed buffer size, q represents the currentamount of buffer consumed by the queued data, and k is a sensitivityexponent. Queued data is advantageously transmitted to the mobilestation based on the scheduling in a multi-user downlink packet on theshared downlink packet data channel. Such an approach allows for delaysensitive data, such as VoIP data, to be scheduled with increasedurgency when quality of service is about to be compromised. The valuedof sensitivity factor k may be modified to increase the effectivecapacity of the packet data traffic channel or to increase quality ofservice to the relevant mobile station. A corresponding apparatus isalso described.

In another embodiment, a scheduler, typically having one or moreprocessing circuits and forming a portion of a base station, attempts topack a multi-user wireless downlink physical layer packet with dataqueued for a plurality of mobile stations using a method that comprises:selecting as a tentative downlink transmission rate a schedulingdownlink transmission rate associated with a primary mobile stationidentified based on a scheduling algorithm; determining if an aggregateamount of data in the packet may be increased by transmitting the packetat a downlink transmission rate lower than the tentative rate; selectinga downlink transmission rate for the packet based on the determining;the packet including data queued for the primary mobile station. Themethod may further comprise selectively adding, based on thedetermining, data queued for at least one additional mobile station tothe packet; the at least one additional mobile station having anassociated scheduling downlink transmission rate lower than thetentative rate. The method may further comprise adding data queued forat least one supplemental mobile station to the packet, the at least onesupplemental mobile station having an associated scheduling downlinktransmission rate that is equal to or higher than the tentative rate.The adding data queued for at least one supplemental mobile station tothe packet may advantageously occur prior to the determining. Thedetermining may comprise calculating a first amount of data to betransmitted in the packet at the tentative rate and comparing the firstamount against a threshold. The threshold typically is a ratio withrespect to a data payload capacity of the packet if transmitted at thetentative rate. Failing to satisfy the threshold typically indicatesthat an aggregate amount of data in the packet may be increased if adownlink transmission rate associated with the packet is lowered. Suchan approach allows for greater link efficiency to be achieved. Acorresponding apparatus is also described.

In another embodiment, a scheduler, typically having one or moreprocessing circuits and forming a portion of a base station, attempts topack a multi-user wireless downlink physical layer packet with dataqueued for a plurality of mobile stations using a method that comprises:selecting a tentative downlink transmission rate and primary mobilestation to be transmitted to for the packet; wherein all of the queueddata for the primary mobile station fails to fill the packet at thetentative downlink transmission rate; determining if data queued for oneor more additional mobile stations could be added to the packet if thedownlink transmission rate was lowered from the tentative downlinktransmission rate to a second downlink transmission rate; and selectinga downlink transmission rate for the packet based on the determining.The method may advantageously comprise selectively adding queued datafor the one or more additional mobile stations to the packet based onthe determining. The determining may comprise identifying one or morecandidate mobile stations having an associated scheduling downlinktransmission rate lower than the tentative downlink transmission rate,such as one step lower than the tentative downlink transmission rate.The determining may comprise comparing an aggregate amount of queueddata allocated to the packet to a data payload capacity of the packet atthe tentative downlink transmission rate. The method may furthercomprise, prior to the determining, adding data queued for a secondmobile station to the packet; the second mobile station having anassociated scheduling downlink transmission rate of at least thetentative downlink transmission rate. The determining may furthercomprise determining if data queued for other mobile stations could beadded to the packet if the downlink transmission rate for the packet waslowered from the second downlink transmission rate to a third downlinktransmission rate lower than the second downlink transmission rate. Acorresponding apparatus is also described.

The above aspects may utilized individually or in combination, as isdesired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary wireless communication network.

FIG. 2 shows an exemplary base station for a mobile communicationnetwork.

FIG. 3 shows exemplary scheduler logic circuits for a wirelesscommunication network.

FIG. 4 shows a flowchart for an exemplary scheduling approach.

FIG. 5 shows a flowchart for an exemplary packing filling process.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates logical entities of an exemplary wirelesscommunication network 10 that provides packet data services to mobilestations 80. FIG. 1 illustrates a wireless communication network 10configured according to the IS-2000 standard. Other standards, including1xEV-DO and WCDMA, could also be employed depending on circumstances.

The wireless communication network 10 is a packet-switched network thatemploys a Forward Traffic Channel (FTC) known as the high-speed forwardpacket data channel (F-PDCH) to transmit data to the mobile stations 80.Wireless communication network 10 comprises a packet-switched corenetwork 20 and a radio access network (RAN) 30. The core network 20includes a Packet Data Serving Node (PDSN) 22 that connects to anexternal packet data network (PDN) 16, such as the Internet, andsupports PPP connections to and from the mobile stations 80. Corenetwork 20 adds and removes IP streams to and from the RAN 30 and routespackets between the external packet data network 16 and the RAN 30.

RAN 30 connects to the core network 20 and gives mobile stations 80access to the core network 20. RAN 30 includes a Packet Control Function(PCF) 32, one or more base station controllers (BSCs) 34 and one or moreradio base stations (RBSs) 36. The primary function of the PCF 32 is toestablish, maintain, and terminate connections to the PDSN 22. The BSCs34 manage radio resources within their respective coverage areas. TheRBSs 36 include the radio equipment for communicating over the airinterface with mobile stations 80. A BSC 34 can manage more than oneRBSs 36. In cdma2000 networks, a BSC 34 and an RBS 36 comprise a basestation 40. The BSC 34 is the control part of the base station 40. TheRBS 36 is the part of the base station 40 that includes the radioequipment and is normally associated with a cell site. In cdma2000networks, a single BSC 34 may function as the control part of multiplebase stations 40. In other network architectures based on otherstandards, the network components comprising the base station 40 may bedifferent but the overall functionality will be the same or similar.

FIG. 2 illustrates exemplary details of a base station 40 in a cdma2000network. The base station components in the exemplary embodiment aredistributed between a RBS 36 and a BSC 34. The RBS 36 includes RFcircuits 42, baseband processing and control circuits 44, and interfacecircuits 46 for communicating with the BSC 34. The RF circuits 42include one or more transmitters 42T and receivers 42R, which transmitsignals to, and receive signals from, the mobile stations 80. Forexample, the receiver 42T receives the channel quality indicators (CQIs)and/or data rate control (DRC) values reported by the mobile stations 80and passes the same on to the baseband processing and control circuits44 for processing. The baseband processing and control circuits 44perform baseband processing of transmitted and received signals. In theembodiment shown in FIG. 2, the baseband processing and control circuit44 includes a scheduler 60 to schedule packet data transmissions on theForward Packet Data Channel (F-PDCH). The baseband processing andcontrol circuit 44 may be implemented in software, hardware, or somecombination of both. For example, the baseband processing and controlcircuit 44 may be implemented as stored program instructions executed byone or more microprocessors or other logic circuits included in RBS 36.

The BSC 34 includes interface circuits 50 for communicating with the RBS36, communication control circuits 52, and interface circuits 54 forcommunicating with the PCF 32. The communication control circuits 52manage the radio and communication resources used by the base station40. The communication control circuits 52 are responsible for settingup, maintaining and tearing down communication channels between the RBS36 and mobile station 80. The communication control circuits 52 may alsoallocate Walsh codes and perform power control functions. Thecommunication control circuits 52 may be implemented in software,hardware, or some combination of both. For example, the communicationcontrol circuits 52 may be implemented as stored program instructionsexecuted by one or more microprocessors or other logic circuits includedin BSC 34.

FIG. 3 illustrates a scheduler 60 according to one exemplary embodimentof the invention. The scheduler 60 makes scheduling decisions andselects the appropriate modulation and coding schemes based on, interalia, channel feedback from the mobile stations 80. The scheduler 60 maybe implemented as one or more processing circuits, comprising hardware,software, or any combination thereof, that are configured as appropriateto implement one or more of the processes described herein. Thescheduler 60 conceptually includes a rate calculator circuit 62 and ascheduling unit circuit 64.

As is customary, the rate calculator 62 receives the channel qualityindicators (CQIs) reported by the mobile stations 80 (step 110) and usesthe CQIs to set a scheduling data transmission rate for each mobilestation 80. Typically, the rate calculator 62 maps the reported CQIvalues to one of a set of predefined modulation and coding schemes,which in turn determines the “scheduling” data rate R for that mobilestation (step 120). Alternatively, the rate calculator 62 may usereported DRC values to determine the scheduling data rate R. Of course,any suitable method for establishing the scheduling data rate R known inthe art may used. The scheduling rate R for each mobile station is inputto the scheduling unit 64 for making scheduling decisions.

The scheduling unit 64 uses a scheduling algorithm to schedule users. Ina broad sense, the scheduling algorithm calculates, at periodicintervals, a rank (or ranking metric) for each mobile station havingqueued data (step 130), and then schedules the transmission of physicallayer packets to those mobile stations based on the ranking metrics.Each mobile station, or class of mobile station (or class of service toa mobile station), may have a different formula for calculating thescheduling ranking metric, see U.S. patent application Ser. No.09/972,793, entitled “System and Methods For User Scheduling in aCommunications Network,” which is incorporated herein by reference. Asan example relevant to the present invention, VoIP users may have aformula for calculating a ranking metric that emphasizes delay on anon-linear basis. In particular, such users may have a ranking metricRANK=R/(d_(max)−d)^(k), where R represents the mobile station'sscheduling downlink transmission rate from the rate calculator 62 (seeabove), d_(max) represents the delay threshold before quality of serviceis expected to become unacceptable due to delay, d represents thecurrent delay, and k is a sensitivity exponent. The delay thresholdd_(max) is established based quality of service considerations,typically by the service provider, based on allowed end-to-end delaybudgets and expected delays elsewhere in the communication path. Thecurrent delay d corresponds to the current amount of delay, or latency,of the data queued for that mobile station. The sensitivity factor khelps establish how sensitive the RANK function is to delay. Thesensitivity factor k may have any positive value, integer or otherwise,with increasing values of k being less sensitive to delay. When thecurrent delay d is substantially less than d_(max), then the RANKformula above acts very much like a maximum throughput ranking formula.However, as the current delay d approaches d_(max), the value of RANKbecomes heavily influenced by the current delay, reaching a maximum whend=d_(max). Thus, when the current delay is high, the value of RANKbecomes relatively higher for a given scheduling transmission rate R.

As pointed out above, the current delay d corresponds to the currentamount of delay, or latency, of the data queued for the particularmobile station of interest. The current delay d may be established in avariety of ways. For example, the current delay d may be the delayexperienced by the oldest data in the relevant queue. Alternatively, thecurrent delay d may be the expected delay, under current or historicalconditions, of the data most recently received into the relevant queue.Of course, other approaches to establishing the current delay d may beused, provided that they correspond to the current amount of delayassociated with the data queued for the particular mobile station ofinterest

If the input rate of the queued data is assumed to be constant, then, asanother method of sensitizing the rank calculation to delay, buffer sizemay be used as a proxy for delay. More particularly, the equation forRANK may be changed to RANK=R/(q_(max)−q)^(k), where R represents themobile station's scheduling downlink transmission rate from the ratecalculator 62 (see above), q_(max) represents the threshold buffer sizefor the queued data before unacceptable degradation in quality ofservice due to delay is expected, q represents the amount of bufferconsumed by the presently queued data for that mobile station, and k isthe sensitivity exponent. Similarly to the above, the maximum allowedbuffer size q_(max) is established based on quality of serviceconsiderations and delay budgets, with an assumption of constant inputrate to the queued data buffer.

For simplicity both delay d and current buffer size q may be referred toas a delay factor. Thus, for both of the above formulas, the value ofRANK for a given scheduling transmission rate R varies directly, butnon-linearly, with an increasing delay factor. Further, both formulasrepresent ways to calculate the ranking metric RANK as a function of thescheduling transmission rate R divided by the difference between athreshold and the delay factor. Also, it should be noted that the valueof the sensitivity factor k need not be constant. Instead, thesensitivity factor k may be adjusted to improve system capacity orquality of service (QoS). The base station 40 may increase the value ofthe sensitivity factor k, making the ranking metric less sensitive todelay for small delays, in order to increase system capacity.Alternatively, the base station 40 may decrease the value of thesensitivity factor k, making the ranking metric more sensitive to delayfor small delays, in order to improve quality of service.

Armed with the ranking metric of each of the mobile stations havingqueued data, the scheduling unit 64 selects the mobile station havingthe highest value of RANK as the mobile station to be transmitted to forthe corresponding physical layer packet on the downlink packet datachannel (step 140). For ease of reference, that mobile station issometimes identified herein as the “primary scheduled mobile station,”or simply “primary mobile station.” The primary mobile station will havean associated scheduling downlink transmission rate R, as discussedabove. For purposes of identification, this rate may be referred to asthe tentative downlink transmission rate, for reasons explained furtherbelow.

In some embodiments of the present invention, the packet is thentransmitted to the primary mobile station at the tentative downlinktransmission rate, in any conventional fashion known in the art (step190). However, in other embodiments, the amount of data queued for theprimary mobile station is evaluated to determine if the correspondingpacket would be full, if transmitted at the tentative downlinktransmission rate, with only data queued for the primary mobile stationincluded in the packet's payload (step 142). If the primary mobilestation has sufficient queued data to fill the packet (if transmitted atthe tentative rate), then the tentative rate is selected as the downlinktransmission rate and the packet is transmitted at that rate. If thedata queued for the primary mobile station is insufficient to fill thepacket, then other queued data is advantageously added to the packet, asdiscussed further below, in order to achieve better overall systemthroughput.

The data added to the packet may first come from data queued for othermobile stations that have an associated scheduling rate R that is thesame as the primary mobile station (step 150). For example, thescheduling unit 64 may evaluate the list of candidate mobile stationshaving queued data in rank order, looking for other mobile stationshaving the same scheduling rate R. If the data queued for such mobilestations, when aggregated with the data for the primary mobile stationalready allocated to the packet, is insufficient to fill the packet, thescheduling unit 64 may expand the search to add mobile terminals withscheduling rates that are higher, by one or more levels, than that ofthe primary mobile station. For ease of reference, the mobile terminalswith both queued data and scheduling rates R of at least as high as theprimary mobile station may be referred to herein as “supplemental mobilestations.” Thus, the packing filing process advantageously looks to fillan otherwise under-filled packet with queued data for other supplementalmobile stations having associated scheduling rates of R (or ≧R).Assuming data is added, the resulting multi-user packet may betransmitted on the downlink packet data channel at rate R to the primaryand supplemental mobile stations. This approach allows the base station40 to more efficiently use the available resources by serving theprimary mobile station and other mobile stations in a multi-user packettransmitted on the downlink packet data channel at rate R.

However, in some instances, the amount of data queued for the primaryand supplemental mobile stations may not be enough to sufficiently fillthe multi-user packet. The present invention, in some embodiments,addresses this situation by conceptually exploring whether more datacould be added to the packet's payload by lowering the downlinktransmission rate to a rate lower than the rate R associated with theprimary mobile station (i.e., the tentative rate)(step 160). Such aprocess may follow the flowchart shown in FIG. 5. The scheduling unit 64calculates the aggregate amount of data allocated to the packet (step210) and compares this to a threshold (step 220). For example, thethreshold may be a ratio of 0.50 for the aggregate amount of datacompared against the capacity Tc of the packet at the tentative rate. Ifthe aggregate amount of data is more than 50%, and thereby satisfiedthreshold, the tentative, the tentative rate is selected as the downlinktransmission rate, and the packet is transmitted at the selected ratewithout adding more queued data to the payload of the packet (step 190).If the aggregate amount of data already allocated to the packet is lessthan 50%, (thereby failing to satisfy the threshold) it is possible thatthe amount of data transmitted in the packet may be increased bylowering the transmission rate, and the process therefore attempts tofind additional queued data to add to the packet. The scheduling unit 64evaluates the list of candidate mobile stations having queued data inrank order, looking for other mobile stations having an associatedachievable rate of the next lower rate R′ than the scheduling rate Rassociated with the primary mobile station (step 230). Assuming thatthere are some such mobile terminals, the scheduler adds their queueddata to the downlink packet (advantageously in rank order) until thepacket is full or the list is exhausted. For ease of reference, themobile stations with lower scheduling rates may be called “additionalmobile stations” in order to distinguish them from the “supplementalmobile stations” with higher scheduling rates. If no queued data foradditional mobile stations may be added to the packet (step 240), thepacket is transmitted at rate R associated with the primary mobilestation (step 190). If, on the other hand, queued data for additionalmobile stations may be added to the packet (step 240), the queued datais added to the packet, the transmission rate is lowered to R′ (step250), and the packet is transmitted at rate R′ (step 190). The result ofthis process, in some embodiments, is to allow significantlyunder-filled packets to have additional queued data added thereto bylowering the anticipated transmission rate for the packet.

In the discussion above, the illustrative threshold was 0.50, but itshould be understood that other threshold values may be used. The valueof 0.50 was used as the illustrative example because it is typical inIS-2000 systems for each rate level to be twice the rate of the nextlower level. Thus, if X amount of data is to be transmitted at rate R,and X is more than ½ of the capacity Tc of the packet at rate R, thencomparing X against 0.50 Tc effectively determines that there will be nonet gain in data transmitted by lowering the rate to R′. Likewise, if Xis less than ½ of Tc, then comparing X against 0.50 Tc suggests thatadditional data may be added to the packet if the transmission rate islowered. However, it should be noted that some systems may have adifferent relation between adjacent rate levels. If so, then thethreshold values should be adjusted accordingly. For example, if eachhigher rate is only 25% more than the next lower rate, then a suitablethreshold value may be ⅘=80%. Of course, the threshold values need nottrack the rate level relationships, but such is believed advantageous.Further, in some embodiments, if the packet still remains significantlyunder-filled, then the process may loop back and repeat steps 210-250one or more times, substituting lowered rate R′ for rate R (step 270)and adjusting the capacity of the packet Tc accordingly (step 280).

As used herein, the term “mobile station” may include a cellularradiotelephone, a Personal Communications System (PCS) terminal that maycombine a cellular radiotelephone with data processing, facsimile, anddata communications capabilities; a Personal Data Assistant (PDA) thatmay include a pager, Web browser, radiotelephone, Internet/intranetaccess, organizer, calendar, and a conventional laptop and/or palmtopreceiver or other appliances that include a radiotelephone transceiver.

The present invention may, of course, be carried out in other specificways than those herein set forth without departing from the scope andessential characteristics of the invention. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive, and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

1. A method of scheduling use of a downlink packet data traffic channelshared by a plurality of mobile stations, comprising: calculating aranking metric for a mobile station that varies directly with the mobilestation's scheduling downlink transmission rate and a delay factorindicative of the staleness of data queued for the mobile station; andscheduling one or more downlink transmissions to the mobile station onthe downlink packet data traffic channel based on said ranking metric.2. The method of claim 1 wherein said calculating said ranking metriccomprises calculating said ranking metric as a function of thescheduling rate divided by the difference between a threshold and thedelay factor.
 3. The method of claim 2 wherein said threshold representsthe maximum allowed delay.
 4. The method of claim 1 wherein said rankingmetric varies in a direct non-linear fashion with the delay factor. 5.The method of claim 1 further comprising determining said delay factorbased on an amount of elapsed time associated with the oldest of thedata queued for said mobile station.
 6. The method of claim 1 whereinsaid ranking metric RANK varies according to the formulaRANK=R/(d_(max)−d)^(k), where R represents the mobile station'sscheduling downlink transmission rate, d_(max) represents the thresholdvalue of the maximum allowed delay, d represents the current delayfactor, and k is a sensitivity exponent.
 7. The method of claim 6wherein k equals one.
 8. The method of claim 6 further comprisingmodifying the value of k upward to increase an effective capacity of thedownlink packet data traffic channel.
 9. The method of claim 6 furthercomprising modifying the value of k downward to increase quality ofservice to said mobile station.
 10. The method of claim 1 furthercomprising determining said delay factor based on an amount of bufferconsumed by said queued data.
 11. The method of claim 1 wherein saidranking metric RANK varies according to the formulaRANK=R/(q_(max)−q)^(k), where R represents the mobile station'sscheduling downlink transmission rate, q_(max) represents the thresholdvalue of the maximum allowed buffer size, q represents the currentamount of buffer consumed by said queued data, and k is a sensitivityexponent.
 12. The method of claim 1: wherein said ranking metric RANKvaries according to the formula RANK=R/(d_(max)−d)^(k), where Rrepresents the mobile station's scheduling downlink transmission rate,d_(max) represents the threshold value of the maximum allowed delay, drepresents the current delay factor, and k is a sensitivity exponent;and further comprising transmitting data to said mobile station based onsaid scheduling in a multi-user downlink packet on the shared downlinkpacket data traffic channel.
 13. A method of packing a multi-userwireless downlink physical layer packet with data queued for a pluralityof mobile stations, comprising: selecting as a tentative downlinktransmission rate a scheduling downlink transmission rate associatedwith a primary mobile station identified based on a schedulingalgorithm; determining if an aggregate amount of data in said packet maybe increased by transmitting said packet at a downlink transmission ratelower than said tentative rate; and selecting a downlink transmissionrate for said packet based on said determining; said packet includingdata queued for said primary mobile station.
 14. The method of claim 13further comprising selectively adding, based on said determining, dataqueued for at least one additional mobile station to said packet; saidat least one additional mobile station having an associated schedulingdownlink transmission rate that is lower than said tentative rate. 15.The method of claim 14 further comprising adding data queued for atleast one supplemental mobile station to said packet, said at least onesupplemental mobile station having an associated scheduling downlinktransmission rate that is equal to or higher than said tentative rate.16. The method of claim 15 wherein said adding data queued for at leastone supplemental mobile station to said packet occurs prior to saiddetermining.
 17. The method of claim 13 wherein said determiningcomprises calculating a first amount of data to be transmitted in saidpacket at said tentative rate and comparing said first amount against athreshold.
 18. The method of claim 17 wherein failing to satisfy saidthreshold indicates that an aggregate amount of data in said packet maybe increased if the downlink transmission rate associated with saidpacket is lowered.
 19. The method of claim 17 wherein said threshold isa ratio with respect to a data payload capacity of said packet iftransmitted at said tentative rate.
 20. The method of claim 13: whereinsaid determining comprises calculating a first amount of data to betransmitted in said packet at said tentative rate and comparing saidfirst amount against a threshold; wherein said threshold is a ratio withrespect to a data payload capacity of said packet if transmitted at saidtentative rate; and further comprising selectively adding, based on saiddetermining, data queued for at least one additional mobile station tosaid packet; said at least one additional mobile station having anassociated scheduling downlink transmission rate that is lower than saidtentative rate.
 21. The method of claim 13 further comprising addingdata queued for at least one supplemental mobile station to said packet,said at least one supplemental mobile station having an associatedscheduling downlink transmission rate that is equal to or higher thansaid tentative rate; wherein said adding data queued for at least onesupplemental mobile station to said packet occurs prior to saiddetermining.
 22. A method of packing a multi-user wireless downlinkphysical layer packet with data queued for a plurality of mobilestations, comprising: selecting a tentative downlink transmission rateand primary mobile station to be transmitted to for the packet; whereinall of the queued data for said primary mobile station fails to fillsaid packet at said tentative downlink transmission rate; determining ifdata queued for one or more additional mobile stations could be added tosaid packet if the downlink transmission rate was lowered from saidtentative downlink transmission rate to a second downlink transmissionrate; and selecting a downlink transmission rate for said packet basedon said determining.
 23. The method of claim 22 further comprisingselectively adding queued data for said one or more additional mobilestations to said packet based on said determining.
 24. The method ofclaim 22 wherein said determining comprises identifying one or morecandidate mobile stations having an associated scheduling downlinktransmission rate lower than said tentative downlink transmission rate.25. The method of claim 24 wherein said candidate mobile stations havean associated scheduling downlink transmission rate that is one steplower than said tentative downlink transmission rate.
 26. The method ofclaim 22 wherein said determining comprises comparing an aggregateamount of queued data allocated to said packet to a capacity of saidpacket at said tentative downlink transmission rate.
 27. The method ofclaim 22 further comprising, prior to said determining: adding dataqueued for a second mobile station to said packet; said second mobilestation having an associated scheduling downlink transmission rate of atleast said tentative downlink transmission rate.
 28. The method of claim22 wherein said determining further comprises determining if furtherdata queued for other mobile stations could be added to said packet ifthe downlink transmission rate for said packet was lowered from saidsecond downlink transmission rate to a third downlink transmission ratelower than said second downlink transmission rate.
 29. The method ofclaim 22: wherein said determining comprises identifying one or morecandidate mobile stations having an associated scheduling downlinktransmission rate lower than said tentative downlink transmission rate;wherein said candidate mobile stations have an associated schedulingdownlink transmission rate that is one step lower than said tentativedownlink transmission rate; wherein said determining further comprisescomparing an aggregate amount of queued data allocated to said packet toa capacity of said packet at said tentative downlink transmission rate;and further comprising selectively adding queued data for said one ormore additional mobile stations to said packet based on saiddetermining.
 30. The method of claim 29 further comprising, prior tosaid determining, adding data queued for a second mobile station to saidpacket; said second mobile station having an associated schedulingdownlink transmission rate of at least said tentative downlinktransmission rate.
 31. The method of claim 30 further comprisingdetermining if further data queued for other mobile stations could beadded to said packet if the downlink transmission rate for said packetwas lowered from said second downlink transmission rate to a thirddownlink transmission rate lower than said second downlink transmissionrate.
 32. A base station for a wireless communications system comprisinga scheduler to schedule use of a downlink packet data traffic channelshared by a plurality of mobile stations, said scheduler comprising oneor more processing circuits configured to: calculate a ranking metricfor a mobile station that varies directly with the mobile station'sscheduling downlink transmission rate and a delay factor indicative ofthe staleness data queued for the mobile station; and schedule one ormore downlink transmissions to the mobile station on the packet datatraffic channel based on said ranking metric.
 33. The base station ofclaim 32 wherein said scheduler is further configured to calculate saidranking metric as a function of the scheduling rate divided by thedifference between a threshold and the delay factor.
 34. The basestation of claim 33 wherein said threshold represents the maximumallowed delay.
 35. The base station of claim 32 wherein said scheduleris further configured to calculate said ranking metric such that saidranking metric varies in a direct non-linear fashion with the delayfactor.
 36. The base station of claim 33 wherein said scheduler isfurther configured to determine said delay factor based on an amount ofelapsed time associated with the oldest of the data queued for saidmobile station.
 37. The base station of claim 32 wherein said scheduleris further configured to calculate said ranking metric RANK according tothe formula RANK=R/(d_(max)−d)^(k), where R represents the mobilestation's scheduling downlink transmission rate, d_(max) represents thethreshold value of the maximum allowed delay, d represents the currentdelay factor, and k is a sensitivity exponent.
 38. The base station ofclaim 37 wherein k equals one.
 39. The base station of claim 37 whereinsaid scheduler is further configured to modify the value of k upward toincrease an effective capacity of the downlink packet data channel. 40.The base station of claim 37 wherein said scheduler is furtherconfigured to modify the value of k downward to increase quality ofservice to said mobile station.
 41. The base station of claim 32 whereinsaid scheduler is further configured to determine said delay factorbased on an amount of buffer consumed by said queued data.
 42. The basestation of claim 32 wherein said scheduler is further configured tocalculate said ranking metric RANK according to the formulaRANK=R/(q_(max)−q)^(k), where R represents the mobile station'sscheduling downlink transmission rate, q_(max) represents the thresholdvalue of the maximum allowed buffer size, q represents the currentamount of buffer consumed by said queued data, and k is a sensitivityexponent.
 43. The base station of claim 32: wherein said scheduler isfurther configured to calculate said ranking metric RANK according tothe formula RANK=R/(d_(max)−d)^(k), where R represents the mobilestation's scheduling downlink transmission rate, d_(max) represents thethreshold value of the maximum allowed delay, d represents the currentdelay factor, and k is a sensitivity exponent; and further comprising atransmitter that transmits data packets to said mobile station based onsaid scheduling in a multi-user downlink packet on the shared downlinkpacket data traffic channel.
 44. A base station for a wirelesscommunications system comprising a scheduler to pack a downlink physicallayer packet with data queued for a plurality of mobile stations, saidscheduler comprising one or more processing circuits configured to:selecting as a tentative downlink transmission rate a schedulingdownlink transmission rate associated with a primary mobile stationidentified based on a scheduling algorithm; determine if an aggregateamount of data in said packet may be increased by transmitting saidpacket at a downlink transmission rate lower than said tentative rate;and select a downlink transmission rate for said packet based on saiddetermination; wherein said packet includes data queued for said primarymobile station.
 45. The base station of claim 44 wherein said scheduleris further configured to selectively add, based on said determination,data queued for at least one additional mobile station to said packet;said at least one additional mobile station having an associatedscheduling downlink transmission rate lower than said tentative rate.46. The base station of claim 45 wherein said scheduler is furtherconfigured to selectively add data queued for at least one supplementalmobile station to said packet, said at least one supplemental mobilestation having an associated scheduling downlink transmission rate thatis equal to or higher than said tentative rate.
 47. The base station ofclaim 46 wherein scheduler is further configured to selectively add saiddata queued for at least one supplemental mobile station to said packetprior to said determination.
 48. The base station of claim 44 whereinscheduler is further configured to calculate, during said determination,a first amount of data to be transmitted in said packet at saidtentative rate and compare said first amount against a threshold.